On Wed, Jan 24, 2018 at 10:59:55AM +0000, Will Deacon wrote: > Hi Paul, > > On Tue, Jan 23, 2018 at 04:00:14PM -0800, Paul E. McKenney wrote: > > On Fri, Jan 19, 2018 at 09:12:11AM -0800, Paul E. McKenney wrote: > > > On Thu, Jan 18, 2018 at 07:58:55PM -0800, Paul E. McKenney wrote: > > > > Hello! > > > > > > > > There is some reason to believe that Documentation/memory-barriers.txt > > > > could use some help, and a major purpose of this patch is to provide > > > > that help in the form of a design-time tool that can produce all valid > > > > executions of a small fragment of concurrent Linux-kernel code, which is > > > > called a "litmus test". This tool's functionality is roughly similar to > > > > a full state-space search. Please note that this is a design-time tool, > > > > not useful for regression testing. However, we hope that the underlying > > > > Linux-kernel memory model will be incorporated into other tools capable > > > > of analyzing large bodies of code for regression-testing purposes. > > > > > > > > The main tool is herd7, together with the linux-kernel.bell, > > > > linux-kernel.cat, linux-kernel.cfg, linux-kernel.def, and lock.cat files > > > > added by this patch. The herd7 executable takes the other files as input, > > > > and all of these files collectively define the Linux-kernel memory memory > > > > model. A brief description of each of these other files is provided > > > > in the README file. Although this tool does have its limitations, > > > > which are documented in the README file, it does improve on the version > > > > reported on in the LWN series (https://lwn.net/Articles/718628/ and > > > > https://lwn.net/Articles/720550/) by supporting locking and arithmetic, > > > > including a much wider variety of read-modify-write atomic operations. > > > > Please note that herd7 is not part of this submission, but is freely > > > > available from http://diy.inria.fr/sources/index.html (and via "git" > > > > at https://github.com/herd/herdtools7). > > > > > > Please note that the latest version of herd is necessary for this version > > > of the memory model. With older versions, you will get error messages > > > like the following: > > > > > > File "./linux-kernel.def", line 44, characters 29-30: unexpected '-' (in macros) > > > > > > Many thanks to Andrea for spotting this one! > > > > And given that I am hearing no objections, I am thinking in terms of > > sending this in a pull request later this week. > > No objections from me. I can't claim to have deep knowledge about everything > being contributed here, but I think that the documentation is well-written > and a welcome addition to the codebase (thanks, Alan!). I also find that, > whilst complicated, the gist of the .cat file comes across pretty well and > is less confusing than the previous situation where we had two .cat files > for the strong and weak models. > > At this stage of maturity, I think that this is all much better as part of > the kernel sources and maintained as such, knowing that things will change > as we encounter new tests and CPU architectures. Sounds very good to me! I just sent a pull request. Wish me luck. ;-) Thanx, Paul
